Hydraulic brake pressure limiting device

ABSTRACT

A pressure limiting device is provided which prevents the output pressure from a power braking system from exceeding the brake line pressure capacity. During normal brake application the pressure limiting device does not function. If hydraulic boost pressure combined with manual operator input force become too great, and brake line pressure exceeds a predetermined value which threatens to rupture the brake line hoses, the limit device functions to prevent further system pressure buildup.

United States Patent Meyers May 23, 1972 54 HYDRAULIC BRAKE PRESSUREFOREIGN PATENTS OR APPLICATIONS LMTING DEVICE 1,032,578 6/1966 GreatBritain ..303/21F [72] Inventor: Robert E. Meyers, South Bend, 1nd.

Primary Examiner--Martin P. Schwadron [73] AssIgnee. The BendixCorporation Assistant Examiner A M. Zupac 22 Filed; 1 1970 Attorney-W.N. Antonis and Plante, Hartz, Smith and Thompson [21] Appl. No.: 89,725

[57] ABSTRACT [52] U.S. C1 ..60/54.5 P, 303/21 F, 91/433 A pressurelimiting device is provided which prevents the out 2; zz g2: putpressure from a power braking system from exceeding the l e o m l brakeline pressure capacity. During normal brake application the pressurelimiting device does not function. If hydraulic [56] References Citedboost pressure combined with manual operator input force UNITED STATESPATENTS become too great, and brake line pressure exceeds apredetermined value which threatens to rupture the brake line hoses,3,578,820 5/1971 Riordan ..303/2l F the limit d i functions to reventfurther system pressure 2,904,960 9/1959 Aikman 1 ..60/54.6 P buildup3,559,532 2/1971 Mac Duff ..303/21 F 2,747,697 5/1956 Banker ..303/21 F8 C1airns, 2 Drawing Figures 32 26 Q i m 22 N1 W HA t l4- 7 m 1 I\RESERVO/ a 1 28 PATENTEDMM23|912 3,664,130

SHEET 2 [1F 2 INVENTOR. ROBERT E. MEYERS ATTORNEYS HYDRAULIC BRAKEPRESSURE LIMITING DEVICE BACKGROUND OF THE INVENTION This inventionrelates to a brake pressure limiting device for 5 use with a vehicularbraking system.

Use of many existing brake pressure boosting devices utilizingmechanical, pneumatic, or hydraulic motive power sources, often causesuch braking systems to be subjected to very high pressures duringemergency braking applications, often much in excess of that needed tocompletely lock the wheels of the vehicle. Small input pressures by thevehicle operator at the brake pedal are multiplied many times by thepressure boosting device, thus sometimes causing brake line pressures tobe precariously near or over the pressure capacities of the brake linehoses. Excessive brake line pressure can rupture them and result inhydraulic fluid loss and attendant loss of braking capability. It istherefore, desirable to provide a pressure limiting device which, whenactuated, will prevent any further output line pressure buildupregardless of the amount of additional pedal pressure applied to thebrakes by the driver; such pressure limit being well in excess of thatrequired to completely lock the wheels of the vehicle under idealbraking conditions.

SUMMARY OF THE INVENTION It is an object of this invention to provide apressure limiting device for a vehicular braking system which, uponactuation at a predetermined brake system pressure, or booster pressurewhich is a function thereof, will prevent excessive brake systempressure buildup, regardless of whether additional brake pedal inputforce is applied, so that brake line hose rupture is avoided.

Another object of this invention is to provide a vehicular brakingsystem with a brake line pressure limiting device which has a minimum ofparts coupled with reliable operation and simplified construction.

Another object of this invention is to provide a brake line pressurelimiting device which can be mounted remotely from other equipment foreasy repair, replacement or maintenance access.

Still another object of the present invention is to effectively limitpressure of one fluid upon signal from a second fluid in a two-fluidsystem without danger of intermixing of the two fluids.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of mypressure limiting device shown in conjunction with a hydraulic brakebooster and associated components of a hydraulic braking system.

FIG. 2 is a similar view showing another embodiment of my invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 fluidpressure is developed in a master cylinder by manually operating a brakepedal 12 which actuates a hydraulic brake booster l4 deriving its motivepower from hydraulic pump 16. Master cylinder 10 could be either of thesingle or split system type for developing pressure in front and rearbraking systems 18 and 20, respectively. Located in the brake booster 14is a spool valve 22 which regulates the pressure in booster chamber 24and thus the magnitude of hydraulic boost assistance by slidably openingand restricting fluid return port 26. This pressure then acts on boosterpiston 17 to assist the vehicle operator in his efforts to apply thebrakes. Lever arm 28, transmits linear motion of the push rod 30 to thespool valve 22 upon operation of pedal 12. Spool valve 22 has anextension 32 which protrudes from the booster for engagement withlinkage 34 as brake line pressures in the braking systems 18 and 20,dictate. Linkage 34 is connected at one end with a brake line pressurelimiting device 36 and at the other end with fixed pivot 37.

The pressure limiting device 36 includes a housing 38 having a firstbore 40 therewithin which communicates with a fluid passage 42 and aspring chamber 46. A second reduced diameter bore 44 also communicateswith bore 40. A piston 48 has a pair of opposing secondary and primaryfaces 50 and 52, respectively, which have differing effective surfaceareas and which, in conjunction with bores 40 and 44 form a pressurechamber 54. Suitable seals 56 and 58 are provided adjacent the pistonface 50 and the piston face 52, respectively, to prevent the escape offluid from the chamber 54. Return spring 60 is located in spring chamber46 and presses against a spring seat 62 which in turn abuts theuniversal end 64 of piston 48. A plug 66 confines the return spring 60in the spring chamber 46 and provides actuating pressure adjustment forthe pressure limiting device 36, by varying the preload on the returnspring 60. Gland 68 guides piston 48 and together with packing 70, sealsthe piston bore 44 from atmospheric contamination. Breather 72 preventsany undesirable pressure or vacuum buildup tending to cause seal 56 toleak. The cavity 74 and spring chamber 46 communicates with atmosphericpressure through the breather 72 and air passage 76. Piston 48 has ashoulder 78 which abuts against the end of gland 68 when the pressurelimiting device is not functioning.

MODE OF OPERATION OF THE PREFERRED EMBODIMENT If there is nooverpressure in the brake systems 18 and 20 and the pressure chamber 54which communicates therewith through fluid passage 42, the piston 48will be held against gland 68 at shoulder 78 by return spring 60.Linkage 34 will be positioned away from spool valve extension 32 and thespool valve 22 will be free to slidably function as necessary to admithydraulic fluid boost pressure from pump 16 to the boost chamber 24which then in turn exerts a force on the piston 17 to assist the vehicleoperator in applying the vehicle brakes.

However, when the pressure in the brake systems 18 and 20 and thepressure chamber 54 exceeds a predetermined value, the force exertedagainst piston face 52 less than that exerted against piston face 50will become great enough to overcome the thrust of the return spring 60,thereby causing the piston 48 to move to the right as viewed in FIG. 1.Linkage 34, which is connected to the piston 48, will then pivot aboutpoint 37 and cause the spool valve extension 32 and the spool valve 22to move toward the right, as viewed in FIG. 1, thus preventing anyfurther restriction of the return port 26 so that the pressure in theboost chamber 24 can increase no more regardless of any additionaleffort exerted by the vehicle operator on the brake pedal 12 If thevehicle operator should manually exert a higher force which threatens torupture the brake lines, the piston 48 will move still further to theright, as viewed in FIG. 1, and, as previously explained, will causefurther pivoting of linkage 34 about pivot 37 and further movement ofthe spool 32 to the right. The pressure in boost chamber 24 will,therefore, be further reduced and will provide a lower force on boosterpiston 17, so that the additional input force by the vehicle operatorwill be effectively offset by the decrease in hydraulic boostassistance, thereby preventing rupturing of the brake lines by limitingthe pressure therein. As the brake line pressures are restored tonormal, spring 60 will cause the piston 48 to move back to the left, asviewed in FIG. 1, thus moving linkage 34 out of contact with the spoolvalve extension 32 so that the spool valve will again be free tomodulate the boost chamber pressure and thus regulate the amount ofpower assistance given to the vehicle operator in applying the brakes,depending upon the force exerted against the pedal.

DESCRIPTION OF THE ALTERNATE EMBODIMENT Referring to FIG. 2, it will beseen that the mechanism operates identically with that illustrated inFIG. 1 and that analogous parts are designated by like numerals plus100. The distinction lies in that pressure from the hydraulic boostchamber 124 is communicated to the pressure chamber 154 of the pressurelimiting device via passages 123 and 142 instead of pressure from thebrake systems 118 and 120.

MODE OF OPERATION OF THE ALTERNATE EMBODIMENT Operation of the alternateembodiment is precisely the same as that of the preferred embodimentwith the exception that the pressure limiting device reacts to apredetermined overpressure in the hydraulic boost chamber to prevent anyfurther pressure increase in the boost chamber.

1 claim:

1. In a braking system having hydraulic brake means, operator-operatedmeans for activating said brake means, and hydraulic power boost meansinterposed therebetween for providing power assist to said operator, apressure limiting device comprising:

a housing having pressure responsive means located therein,

said pressure responsive means being operatively connected to one ofsaid hydraulic means and being movably responsive to hydraulic pressurestherein above a predetermined value; and

lever means operatively connected to said pressure responsive means andto said power boost means for limiting the output of said power boostmeans upon movement of said pressure responsive means.

2. A pressure limiting device, as defined in claim 1, wherein saidpressure responsive means is operatively connected to said hydraulicbrake means.

3. A pressure limiting device, as defined in claim 1, wherein saidpressure responsive means is operatively connected to said hydraulicpower boost means.

4 A pressure limiting device, as defined in claim 1, wherein saidhousing includes a fluid passage, a first bore. and a second bore havinga different diameter communicating with said first bore;

said pressure responsive means includes a piston slidably mounted insaid first and second bores having a pair of opposed faces with unequalsurface areas;

said first and second bores and said opposed faces comprising a chambercommunicating with said fluid passage.

5. A pressure limiting device, as defined in claim 4, wherein:

said power boost means includes a valve for controlling the power outputthereof;

said lever means being operatively connected to said piston forcontrolling movement of said valve.

6. A pressure limiting device, as defined in claim 1, which includesresilient means located in said housing for opposing movement of saidpressure responsive means, and adjustment means operatively connected tosaid resilient means for varying said predetermined value.

7. A pressure limiting device as claimed in claim 5, wherein said levermeans has one end thereof attached to said piston and the other endthereof pivotally connected to a fixed point, and said valve includes aprojection for engagement with said lever means intermediate the endsthereof.

8. A pressure limiting device as defined in claim 6 wherein saidadjustment means includes a plug threadedly installed in said housingand abutting said resilient means for varying the preload exertedthereby.

1. In a braking system having hydraulic brake means, operatoroperatedmeans for activating said brake means, and hydraulic power boost meansinterposed therebetween for providing power assist to said operator, apressure limiting device comprising: a housing having pressureresponsive means located therein, said pressure responsive means beingoperatively connected to one of said hydraulic means and being movablyresponsive to hydraulic pressures therein above a predetermined value;and lever means operatively connected to said pressure responsive meansand to said power boost means for limiting the output of said powerboost means upon movement of said pressure responsive means.
 2. Apressure limiting device, as defined in claim 1, wherein said pressureresponsive means is operatively connected to said hydraulic brake means.3. A pressure limiting device, as defined in claim 1, wherein saidpressure responsive means is operatively connected to said hydraulicpower boost means.
 4. A pressure limiting device, as defined in claim 1,wherein said housing includes a fluid passage, a first bore, and asecond bore having a different diameter communicating with said firstbore; said pressure responsive means includes a piston slidably mountedin said first and second bores having a pair of opposed faces withunequal surface areas; said first and second bores and said opposedfaces comprising a chamber communicating with said fluid passage.
 5. Apressure limiting device, as defined in claim 4, wherein: said powerboost means includes a valve for controlling the power output thereof;said lever means being operatively connected to said piston forcontrolling movement of said valve.
 6. A pressure limiting device, asdefined in claim 1, which includes resilient means located in saidhousing for opposing movement of said pressure responsive means, andadjustment means operatively connected to said resilient means forvarying said predetermined value.
 7. A pressure limiting device asclaimed in claim 5, wherein said lever means has one end thereofattached to said piston and the other end thereof pivotally connected toa fixed point, and said valve includes a projection for engagement withsaid lever means intermediate the ends thereof.
 8. A pressure limitingdevice as defined in claim 6 wherein said adjustment means includes aplug threadedly installed in said housing and abutting said resilientmeans for varying the preload exerted thereby.